It is well known that water soluble film material such as polyvinyl alcohol or methylhydroxylpropyl cellulose, for example, can be used to form the walls of a water soluble container or package. Typically, such a container is filled with a liquid or solid water soluble or dispersable substance and sealed, thus forming a package that dissolves completely when immersed in water.
Water soluble packaging has many advantageous commercial applications. For example, water soluble packaging is frequently used to contain potentially harmful materials, such as pesticides, which are produced as concentrated solutions or powders that must be dispersed in water or other organic liquid before use. Packaging such materials in water soluble containers overcomes many potential hazards. First, because water soluble packaging is pre-sealed, there are no airborne particles that could be ingested by, or otherwise contact, the user in contrast with conventional packaging which must be opened prior to use. Second, water soluble packages are filled with precise quantities of the chemical, thereby preventing waste through over charging or under charging. Finally, water soluble packaging is biodegradable and dissolves completely in water so that there is no potentially hazardous or environmentally destructive packaging material to be discarded.
Water soluble containers are typically formed by large, single unit packaging machines. In such machinery, large rolls of water soluble film are unwound into a web and transported by rollers toward a forming station where segments of the film web are folded into the shape of a container, sealed on the bottom and sides, filled with water soluble material and sealed at the top to form a leak-proof container. Because environmental conditions can adversely affect the properties of most water soluble films, the packaging machines are usually placed in special rooms where temperature and relative humidity are carefully controlled according to the film manufacturer's specifications.
It is highly desirable that the outside of the water soluble package be labeled with manufacturer's indicia or other consumer information. Indeed, where the packaging contains hazardous materials, informational labeling, such as instructions for use of the article or safety warnings, may actually be required by law or by regulatory agencies. Other indicia, such as article identification or the manufacturer's name and trademarks, provide the consumer with useful, and often necessary, information about the article. In addition, it is desirable that such information be printed directly on the outside walls of the container rather than on separate paper or other labels that are affixed to, and thus become part of, the container, thereby rendering the container partially insoluble.
Typically, direct labeling of water soluble packages is accomplished by printing on the water soluble film material in a special process before the film is installed on a packaging machine. In many instances, the pre-printing process requires rolls of water soluble film to be unwound, printed using an ink jet printer or other process such as flexography or heliography, and then heated so that the ink will dry on the film. The film is then rewound into rolls and delivered to the packaging process.
There are, however, a number of drawbacks associated with this printing method. First, this printing process requires the use of non-water soluble ink which can interfere with the solubility of the container walls when used. Second, it is difficult to print graphics using this method. Third, applying heat to dry the ink on the film can adversely affect the solubility of the packaging material. Finally, this separate, off-line printing process requires extra handling of the material which adds significantly to the cost of producing water soluble packages.
Thus, there has been a need for a method and apparatus for printing text and graphics on water soluble films that does not interfere with the characteristics of the material and which minimizes handling and disruption of the packaging process. Furthermore, there has been a need for an in-line printing process that can be installed with and operate in-line with a standard water soluble film packaging machine.